Vulcanization of rubber



Patented Apr. 30, 1940 VULCANIZATION OF RUBBER I tion of New YorkApplication April 27, 1538, Serial No. 204,556

16 Claims.

This invention relates to the vulcanization of rubber, and to a methodwhereby vulcanization of rubber at processing temperatures may beprevented.

It has long been known that dialkyl dithiocarbamates are acceleratorscausing rapid vulcanization at such low temperatures that it has beendifficult to employ them commercially. This tendency to prevulcanize orscorch has been corrected to some extent by substituting thecorresponding diaryl compounds. Even the diaryl compounds may scorch,however, if stocks containing large amounts are masticated or other-.wise processed at temperatures as high as 240 C.

It is an object of this invention accordingly to provide delayed actionaccelerator combinations which, when included therein, reduce thetendency of compositions containing certain diaryl dithiocarbamates toscorch at processing temperatures without retarding the vulcanization atouring temperatures. Other objects are to reduce the total acceleratorconcentration in rubber compositions with a consequent reduction incost, and to provide vulcanized rubber compositions having greaterresistance to deterioration, lower hysteresis, and betterflex-resistance than compositions vulcanized in the conventional manner.

I have discovered that the activity of accelerators of the classconsisting of diaryl dithiocarbamic acids, their salts, and their estersat processing temperatures is greatly reduced in the presence of amember of the class consisting of mercapto thiazoles and dithiazylsulfides. This delayed action is particularly surprising in view of thefact that these latter compounds are vigorous accelerators themselves.Suitable accelerators which may be used in the delayed actionaccelerator combinations of this invention include, accordingly, freeacids such as diphenyl dithiocarbamic acid or the similar ditolyl(ortho, meta, para or mixed), dinaphthyl (alpha, beta or mixed),dixenyl, dianthryl, diphenanthryl, diindenyl, phenyl-naphthyl,phenyl-xenyl, phenylcumyl, di p nitrophenyl, di p chlorphenyl, phenyl mbromphenyl, di p hydroxyphenyl, phenyl-p-phenyloxyphenyl, phenyl panilinophenyl, di o anisyl, phenyl p methylaminophenyl, or other likediaryl dithiocarbamic acids; salts of diaryl dithiocarbamic acids suchas metal salts like sodium or zinc diphenyl dithiocarbamate, andammonium salts like trimethylammonium diphenyl dithiocarbamate,particularly quaternary ammonium salts such as benzylhexamethylenetetrammonium diphenyl dithiocarbamate and methylhexamethylenetetrammonium diphenyl dithiocarbamate; and esters of diaryldithiocarbamic acid including tris (diaryle dithiocarbamylalkyl) aminessuch as tris (diphenyldit ioc amylm t rl am ne. W1l 9h;-. S

carbamate, etc.

an ester of trimethanolamine), and polynitroaryl esters such as 2,4dinithrophenyl diphenyl dithio- Other examples of accelerators UNITEDSTATES iPAT E NT OFFICE,

which may be advantageously used with the de- I layed actionaccelerators of this invention are Semon Sept. 15, 1937, Serial No.163,989 filed by Semon Sept. 15, 1937, Serial No. 163,991 filed by SloanSept. 15, 1937, and Serial No. 164,013 filed by Semon Sept. 15, 1937.

A wide range of thiazole accelerators may be used to form the delayedaction accelerator combinations of this invention. Illustrative of thetypes of compounds which may be used are 2 mercaptobenzothiazole, 2mercaptonaphthothiazole, 2 mercapto-4-methylthiazole, 2-mercapto 4,5dimethylthiazole, 2 mercapto 4 methyl-5-ethylthiazole and similar alkylor arylene mercaptothiazoles and the corresponding dithiazyl sulfidesincluding the monoand polysulfides such asdibenzothiazyl disulfide,dibenzothiazyl tetras ulfide, bis-4,5-dimethylthiazyl monosulfide,bis-4,5-dimenthylthiazyl disulfide, etc. The two types of acceleratorsare usually mixed in proportions varying from 1:3 to 3:1 parts byweight.

The beneficial results obtained by practicing the method of thisinvention'may be better understood by reference to the accompanyingdrawing of which 7 Fig. 1 represents graphically the acceleratingproperties of a combination of Z-mercaptobenzotris(diphenyldithiocarbamyl- Parts by weight Rubber Carbon black 40 Sulfur 3Stearic acid 2 Phenyl-beta-naphthyl amine 0.75 Zinc oxide a 5 Softeners2 Tris (diphenyl dithiocarbamylmethyl) amine 0.5

1 Curve B represents the rate of cure at 240 F. of the above compositioncontaining in addition 10. The process which comprises vulcanizingrubber in the presence of 2-mercaptobenzothiazole and a; diaryldithiocarbamate.

11. The process which comprises vulcanizing rubber in the presence "oftris(dipheny1-dithiocarbamylmethyl) amine and. Z-mercaptobenzothiazole.

12. A rubber composition which'hes been vulcanized in the presence of a.member of the class rubber in the presence of a member of the classconsisting of diaryidithiocarbamic acids, their salts, and their estersand a member of the class consisting of mercaptothiazoles and thiazylsulfides. I

13. A rubber composition Which hasbeen Vulcanized in the presence ofbenzyl hexamethylenetetrammonium diphenyl dithiccerbamete anddibenzothiazyl disulfide'. J t I 14. A rubber "composition which hasbeen vulcanized in the presence of tris(dipheny1dithiocarbamylmethyi) arlines and bis-4,5-dimethy1-fl thiazyl disuifide. v

15. A rubber composition which has been vulcanized in the presence oftris(-dipheny1dithiocarbamylmethyl) amine and 2-mercaptobenzothiaatzole."16.The process which comprises vuicanizing consisting of diaryldithiocarbamic acids; their salts, andthei'r esters and a member of theclass consisting of mercaptothiazoles and dithiazyl sulfides inproportions from 1:3 to 3:1;

' PAUL c. JONES.

